Need fuel regulator advice - Radical cam - 78 280Z

[bmuu]

I recently acquired a 1978 280Z which incorporates a 512 / 300 high lift, long duration cam. In addition, the engine is outfitted with a custom fuel rail and high flow / pressure injectors (29lb). The original fuel pump has been replaced with a unit that has a deadhead pressure of approximately 100lb.

The problem I’m having is that the fuel pressure regulator is a stock unit. Among other problems, it is incapable of dealing with the high pressure and low manifold vacuum at idle. The biggest problem I’m having is that due to the high duration cam, the vacuum is less than 5 in-Hg while idling. As a result the regulator senses that the car is accelerating and causes it to run so rich that it will barely idle without stalling. If it does stall it totally soaks the plugs and makes restarting extremely difficult, or impossible without removing and drying the plugs.

I know there are several adjustable / programmable regulators available, but I’m not sure how they get around the low vacuum at idle. This must be a fairly common problem, as there are a lot of performance cars with radical cams, but after a whole lot of searching, I’ve not been able to find a solution. Any help or suggestions would be greatly appreciated.

Thanks.

[FastWoman]

For the most part, what determines your fuel delivery is the air flow through the air flow meter, the readings of the other sensors (for fine tuning). The ECU does its computations based on these, and it delivers a pulse width to the injectors that is directly proportional to the amount of fuel to be delivered. If it's functioning properly, the fuel pressure regulator maintains a constant pressure differential between the fuel rail and the intake manifold. That constant differential results in a known delivery of fuel for a given pulse width. If your manifold vacuum is low, the pressure should regulate higher, so as to deliver that constant flow rate.

Your system has so many mods that I wouldn't really know where to begin with it. However, the fact that the injectors are "high flow/pressure injectors" suggests to me that their flow rate is foreign to the ECU. I think that's a huge potential problem, and you should verify that the injectors deliver fuel at a roughly ordinary rate when switched on.

Before you invest lots of time in pursuing that avenue, however, I'd check the connection to the coolant temperature sensor. If you have a bad connection there (or a bad/open sensor), you'll experience EXTREMELY rich running -- black smoke out the tail pipe, very bad idle, etc. -- just as you've described. Those electrical connectors get pretty crumbly, especially on the front of the engine. I think you would learn the most by pulling the connector off of your ECU (and not touching the temp sensor yet). Measure for conductivity between pin 13 and ground. It should be in the neighborhood of a couple of kohms cold, give or take, depending on temperature. If you read an open circuit, there's your problem. You'll probably need to clean up the connector to the water temp sensor (the smaller of the sensors in your thermo housing with two wires -- not the one with the single wire).

The other place I'd look is your cold start valve. It might be stuck open, or the thermotime switch (the other two-wire plug in the thermo housing) might be having issues.

Anyway, I really doubt the radical cam is to blame for the rich running. The pump may be rather high pressure, but I suspect the fuel pressure regulator can handle it. (Just measure the fuel pressure to be certain!) As far as you know, did the modified engine ever run right?

[zKars]

Hmmmm... 300 cc/min injectors on engine designed for 185cc/m injectors. Maybe the fuel pressure regulator is not the only reason for running a tad rich....... Just thinking out loud here....

Your not going to get control of your fueling problems with the stock EFI system.

[bmuu]

I am far from an expert when it comes to fuel injected engines, but I thought one of the functions of the pressure regulator was to reduce the fuel pressure to the injectors while the car was at idle (high manifold vacuum). In other words, given a certain pulse width and slope at the injectors, lower fuel pressure would result in less fuel being delivered the cylinders and a leaner mixture.

As far as the temperature sensors are concerned, been there – done that. I do not know how a stock 280Z behaves, but in my case if the connection to the water temperature sensor feeding the ECU is removed (open circuit), the engine goes so rich that it will barely run at any throttle setting, much less idle. When I first got the car, it would intermittently stall while idling, just as if someone had turned the key off. After checking everything from the coil to the fuel injector relay, I discovered that the Bosch plug at the temperature sensor, had a broken / intermittent connection. After replacing the plug and substituting soldered connections for the bullet connectors, that problem was resolved. The start injector has been removed, so the thermotime sensor is irrelevant.

[cozye]

You will never get high vacuum from a radical cam, so the stock FPR will never get the correct fuel pressure. Additionally you have higher flow rate injectors, which will flow more fuel for the same pulse signal designed for the lower fuel rate injectors. It's a known fact that the bosch EFI system on these cars does not have any good method for tuning a modified motor. You will never get this car running right with that cam, those injectors, on the stock EFI. You have two options.

Option A, put the stock cam and injectors in the car

Option B, go to meqasquirt ECU and then you can tune whatever fuel rate you want.

If you do some searches, especially over on zcar.com and hybridz, you will find that 100% for sure you can't tune the EFI to do what you are trying to do. This system is not a closed loop system and doesn't have any reliable means for adjusting air fuel ratio. It was specifically designed for the stock setup and doesn't have any significant tuning capability.

And FWIW, on the stock motor you can remove all vacuum to the FPR so that you are getting 37psi on the rail, and the car doesn't run that rich. So I'm thinking that even if you try to get your current setup to half way run, mucking with the FPR isn't going to get you where you need to be.

[FastWoman]

Bmuu, the pressure regulator does drop fuel pressure at high vacuum (e.g. at idle), but only because it is maintaining a constant pressure differential between the fuel rail and intake manifold. It's nothing more complicated than that. If you have a high engine vacuum and no compensation for that in the fuel pressure, then the gas is going to be sucked out of the injectors at a higher rate. All the regulator does is to keep the fuel delivery rate constant, so that the ECU can regulate delivery in terms of pulse width.

I tend to agree with Jim and Coz (Eric). As your system is configured, you're probably going to have to go with a non-stock ECU, like a MegaSquirt system. Either that, or you're going to have to revert back to stock injectors. (I admittedly don't know what to expect from that cam on an EFI system.) FAIW, I'm running these right now, and they work fine:

http://cgi.ebay.com/ebaymotors/75-76-77-78-79-80-81-82-83-Datsun-280Z-Fuel-Injectors-_W0QQcmdZViewItemQQhashZitem255f93698eQQitemZ160517286286QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

Important question, though: As far as you know, did the engine ever run correctly with this configuration, or was it a project gone wrong and sold cheaply to someone else? Knowing this answer will make all the difference in how you should approach correcting your current problem.

Anyway, that's about the extent of the advice I can offer. If you want to keep the modified configuration, your best advice is probably going to come from the HybridZ forum, 'cuz they do that sort of stuff all the time.

Edited December 10, 2010 by FastWoman

[bmuu]

Bmuu, the pressure regulator does drop fuel pressure at high vacuum (e.g. at idle), but only because it is maintaining a constant pressure differential between the fuel rail and intake manifold. It's nothing more complicated than that. If you have a high engine vacuum and no compensation for that in the fuel pressure, then the gas is going to be sucked out of the injectors at a higher rate. All the regulator does is to keep the fuel delivery rate constant, so that the ECU can regulate delivery in terms of pulse width.

I tend to agree with Jim and Coz (Eric). As your system is configured, you're probably going to have to go with a non-stock ECU, like a MegaSquirt system. Either that, or you're going to have to revert back to stock injectors. (I admittedly don't know what to expect from that cam on an EFI system.) FAIW, I'm running these right now, and they work fine:

http://cgi.ebay.com/ebaymotors/75-76-77-78-79-80-81-82-83-Datsun-280Z-Fuel-Injectors-_W0QQcmdZViewItemQQhashZitem255f93698eQQitemZ160517286286QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

Important question, though: As far as you know, did the engine ever run correctly with this configuration, or was it a project gone wrong and sold cheaply to someone else? Knowing this answer will make all the difference in how you should approach correcting your current problem.

Anyway, that's about the extent of the advice I can offer. If you want to keep the modified configuration, your best advice is probably going to come from the HybridZ forum, 'cuz they do that sort of stuff all the time.

In answer to the last part of your question, “As far as you know, did the engine ever run correctly with this configuration . . .” I really don’t know for sure, but I suspect not. A bit of history may help. I purchased this car, sight unseen, off the internet (yea, I know, big mistake). Originally, about 10 years ago, the car underwent a complete restoration, including extensive under-hood modifications. In addition to the cam and fuel system modifications, a large bore throttle body and 280ZX AFM were installed at the same time. I think the guy who owned it at the time was more interested in winning car shows than having a reliable driver. In fact, between 2000 – 4 the car won several awards at various So-Cal shows. Back in the day, we used to say, “If it don’t go, chrome it”. I think that may have been the case here.

As far as the ECU is concerned, I understand what you, Jim and Coz are saying. In fact I looked at the Megasquirt, but I wasn’t sure how it would work in my case, due to the total lack of sensors on the ’78 280Z (MAP, O2, etc.).

At this point I starting to wonder what I would gain if I just went back to the stock injectors. I assume the ones you linked to on your last post are basically stock.

[FastWoman]

Yeah, basically stock -- just not OEM Nissan. If I were you, I think I'd try stock injectors [EDIT: AND AFM) as a first stab at the problem. Forget about the cam, throttle body, and 100 psi pump for now. I don't think those are going to affect your mix. Just leave 'em and see what happens. (But of course verify your fuel pressure to make certain the pump isn't too much!)

If you want to consider Megasquirt, you can probably cobble a MAP to the intake and an O2 sensor to the exhaust. (A muffler shop should be able to weld a fitting into your exhaust for the sensor.)

I suppose the route you take depends a bit on what you want to do with the car. If you just want to drive it, the easiest route would probably be to revert to stock. If you want to race it, then you may want to keep the mods. The stock injectors might not put out enough fuel to keep up with the cam at high RPMs and WOT. Your mixture might end up too lean, which definitely isn't good. In that case the injectors you have, controlled by a Megasquirt system, might be the better route.

Edited December 10, 2010 by FastWoman

[cozye]

Do you know what other engine mods were done ? Exhaust, intake, head, compression etc.. ? It has to be a whole plan. I think if the engine has been modified extensively, the stock injectors may help, but it won't get you where you need to be. If the only thing that has been done is to put the wrong AFM on, and a big cam with large injectors, I think you have to go back to stock all the way. It's not hard to put a cam on these motors.

If it were me, I'd probably just give megasquirt a shot. I've done quite a bit of research. All you will need is the ecu, and a intake air temp sensor, and ideally an o2 sensor. The megasquirt has a map sensor built in the ecu. You would no longer need your AFM (you don't have the right one anyway). Tuning the MS system would not be difficult and there is a plethora of information out there as well as base maps to get you started. With the o2 sensor you can get it tuned perfectly in short order.

[bmuu]

Yeah, basically stock -- just not OEM Nissan. If I were you, I think I'd try stock injectors as a first stab at the problem. Forget about the cam, throttle body, and 100 psi pump for now. I don't think those are going to affect your mix. Just leave 'em and see what happens. (But of course verify your fuel pressure to make certain the pump isn't too much!)

If you want to consider Megasquirt, you can probably cobble a MAP to the intake and an O2 sensor to the exhaust. (A muffler shop should be able to weld a fitting into your exhaust for the sensor.)

I suppose the route you take depends a bit on what you want to do with the car. If you just want to drive it, the easiest route would probably be to revert to stock. If you want to race it, then you may want to keep the mods. The stock injectors might not put out enough fuel to keep up with the cam at high RPMs and WOT. Your mixture might end up too lean, which definitely isn't good. In that case the injectors you have, controlled by a Megasquirt system, might be the better route.

Thanks for the help. I don't want to race the car, but on the other hand to take it back to stock would probably cost me just as much as upgrading the ECU or replacing the injectors. I'm kind of on a journey here and I've got to figure out if I'm closer to home (stock) or my final destination (finish the mods). As it is the car is probably closer to a race configuration than stock. In addition to the mods I've already mentioned, the engine has been bored 30 over, has a balanced crank, stainless valves, hardened valve seats and springs, ported, polished and matched intake, 3" exhaust headers - tail pipe, custom drive train mods and etc.

With that thought in mind, I think I'll take your advise and upload my original posting to the HybridZ forum.

Thanks everyone for the ideas and suggestions.

[bmuu]

Do you know what other engine mods were done ? Exhaust, intake, head, compression etc.. ? It has to be a whole plan. I think if the engine has been modified extensively, the stock injectors may help, but it won't get you where you need to be. If the only thing that has been done is to put the wrong AFM on, and a big cam with large injectors, I think you have to go back to stock all the way. It's not hard to put a cam on these motors.

If it were me, I'd probably just give megasquirt a shot. I've done quite a bit of research. All you will need is the ecu, and a intake air temp sensor, and ideally an o2 sensor. The megasquirt has a map sensor built in the ecu. You would no longer need your AFM (you don't have the right one anyway). Tuning the MS system would not be difficult and there is a plethora of information out there as well as base maps to get you started. With the o2 sensor you can get it tuned perfectly in short order.

If I understand what you're saying, all that would be required to install the Megasquirt would be to install an O2 sensor along with an intake air sensor. I understand what it takes to install an o2 sensor, but I'm not sure what type of air temp sensor you're referring to. Would this be the same type of temp sensor that is part of the AFM? Where and how would it be installed?

As you can see by my previous post, this engine has extensive mods that might make it worth the effort to replace the ECU and do it right. The more I think about it, going back to stock would be a waste of all the work the original owner did. FWIW, the car has never been raced and has less than 5,000 miles on the engine.

Thanks.

[cozye]

If I understand what you're saying, all that would be required to install the Megasquirt would be to install an O2 sensor along with an intake air sensor. I understand what it takes to install an o2 sensor, but I'm not sure what type of air temp sensor you're referring to. Would this be the same type of temp sensor that is part of the AFM? Where and how would it be installed?

As you can see by my previous post, this engine has extensive mods that might make it worth the effort to replace the ECU and do it right. The more I think about it, going back to stock would be a waste of all the work the original owner did. FWIW, the car has never been raced and has less than 5,000 miles on the engine.

Thanks.

Megasquirt is a great way to go and very popular. I'm considering doing it even on my stock car just due to the fact that it is a much more modern, tuneable, and better EFI setup.

IAT, intake air temp sensor. All you need to do is thread like a 3/8 whole in the intake manifold and screw in the sensor. Some people use the cold start valve hole and thread that. The most common is the GM sensor, and they are cheap. You can get one with your megasquirt. The megasquirt will primarily read MAP, and IAT sensors for input, and o2 can be configured for logging only, or closed loop operation. You don't even need a TPS if you don't want.

I would SERIOUSLY consider going this route. Wouldn't cost you more than $400 tops.

The only draw back is that MS is an open system, so there are dozens of methods to set it up. You can control ignition with it etc.. too .It can get a bit confusing at first. I'm still trying to learn about it before making my jump to it. Just keep it simple at first I would think. Do fuel only. Go to www.diyautotune.com for more info. Hybridz.org has a whole forum dedicated to EFI management using megasquirt. Just go lurk there to make sense of it.

I am very familiar with EFI management on race motorcycles as I've used it for years. Basically once you have your system installed, you can build your map or fuel table in a 2 axis grid. On the bikes we log the data with the o2 sensor and just change the values in the cells until we hit the target air fuel ratio. It's simple. Bikes can't do closed loop though because they rev to fast and the wideband can't keep up.

edit.. on the extensive mods, i was refering to more than the fuel injectors. If the PO didn't build the head and intake, and bump the compression some to go along with that big cam, it may not ever get where you want it to be.

Edited December 10, 2010 by cozye